Manchester United have stepped up attempts to bolster their defence with an offer for Bayern Munich pair Matthijs de Ligt and Noussair Mazraoui, a source has told ESPN.

De Ligt and Mazraoui are available this summer with Bayern valuing the pair at a combined 55 million ($70.4m). United's bid has fallen below that valuation and is set to be rejected by the Bundesliga side.

Manager Erik ten Hag is keen to add another centre-back and a full-back to his squad before the transfer deadline.

Leny Yoro, a 52m summer signing from Lille, has been ruled out for three months with a broken foot while left-back Tyrell Malacia is not expected back for another two months as he continues his comeback from a knee injury.

Sources have told ESPN that United's plan was always to pursue further defensive additions and the formal contact with Bayern has not been prompted by Yoro's injury.

There remains interest in Jarrad Branthwaite, who can play at centre-back and left-back, although Everton's valuation of more than 70m is proving problematic. United have already seen two offers rejected by Everton.

Despite spending more than 85m to bring in Yoro and striker Joshua Zirkzee this summer, United have been able to table a significant offer to Bayern because of growing confidence that Aaron Wan-Bissaka will complete a move to West Ham.

United value the right-back at between 15m to 20m and an agreement with West Ham is moving closer. West Ham had shown interest in Mazraoui before a deal collapsed.

A source has told ESPN that both De Ligt and Mazraoui are keen to move to Old Trafford if the two clubs can agree a deal.